Determining the content of chemical elements or isotopes thereof in a specimen by utilizing the effect of recoilless resonance absorption or scattering of gamma rays

ABSTRACT

An arrangement and process for determining the content of chemical elements, isotopes or compounds thereof in a specimen comprising the measurement during irradiation of the specimen with gamma-rays of a quantity that is proportional to the content of the element, isotope or compound in the specimen.

United States Patent Moscow, U.S.S.R. [21] Appl. No. 619,290 [22] FiledFeb. 28, I967 [45] Patented Aug. 3, I971 [54] DETERMINING THE CONTENT OFCHEMICAL ELEMENTS OR ISOTOPES THEREOF IN A SPECIMEN BY UTILIZING THEEFFECT OF RECOILLESS RESONANCE ABSORPTION OR SCATTERING 0F GAMMA RAYS 6Claims, 3 Drawing Figs.

[52] US. Cl 250/833, 250/83;84

I!!!III!IIIIIIIIII/IIIl/IIr/IA [51] Int. Cl 601i 1/16 [50] FieldotSearch 250/83. 83.3.84,106S

[56] References Cited UNITED STATES PATENTS 3,193,683 7/1965 Reiffel250/106 S 3,257,558 6/1966 Cook et a1. 250/833 OTHER REFERENCES Usingthe Mossbauer Effect, by V. I. Goldanskii, from International ScienceAnd Technology, December [963, pgs. 40 to 48; 25084 PrimaryExaminer-Archie R. Borchelt Anomey-Holman, Glascock, Downing and SeeboldABSTRACT: An arrangement and process for determining the content ofchemical elements, isotopes or compounds thereof in a specimencomprising the measurement during irradiation of the specimen withgamma-rays of a quantity that is proportional to the content of theelement, isotope or compound in the specimen.

' PATENTEU M 3m SHEET 1 BF 2 FIG! BACKGROUND OF INVENTION This inventionrelates to a method of determining the content of chemical elements,isotopes or compounds thereof in diverse specimens, and also relates toan arrangement for accomplishing said method.

It is known to determine the content of chemical elements in specimensby determination of the characteristic X-radia tion of the element beinganalyzed in the specimen.

Said method makes use of X-ray equipment or gamma-ray sources whichexcite the characteristic X-radiation, and devices for analysis of theX-ray spectra thus produced.

It is also known to determine the content of chemical elements orisotopes thereof from the induced activity produced by irradiating thespecimen under investigation with neutrons or gamma-quanta.

In said method recourse is bad to neutron or gamma-ray sources forirradiating the test specimen, and devices for analyzing the gamma-rayspectrum thus obtained.

It is also known to evaluate chemical elements in solids by irradiatinga solid specimen with gamma-rays that undergo resonance absorption orscattering on an impact with isotope of the element being analyzed,simultaneously determining the difference in the count rates ofresonance gamma-rays, said difference corresponding to two differentstates of the relative motion of the gamma-ray source and solidspecimen, and thereafter evaluating the chemical element in the solidspecimen from the difference in count rates.

Said techniques involves the employment of devices comprising aresonance gamma-ray source, a gamma-ray detector, a mechanism foreffecting the displacement ofthe gamma-ray source and test specimen inrelation to each other, and a recording unit. I

These prior art methods of chemical element analysis suffer fromdrawbacks in that the results of measurements depend upon thecomposition of test specimens, that said methods provide no means ofdetermining various chemical compounds of the elements being analyzed,and that a special procedure is required for preparing test specimens.

Moreover, known devices for the accomplishment of said methods, areintricate, cumbersome, and in many cases inconvenient in operation,particularly under field conditions.

It is an object of the present invention to eliminate said drawbacks.

It is another object of the present invention to provide a method fordetermining the content of chemical elements,

isotopes or compounds thereof in diverse specimens, and an arrangementfor accomplishing said method, said method and I arrangement being notedfor their high precision and scnsitivi' y- It is a further object of thepresent invention to provide in arrangement for determining the contentof chemical elements in specimens irrespective of the composition ofsaid specimens.

It is an additional object of the present invention to provide anarrangement for determining the content of chemical elements inspecimens so as to leave the specimens intact.

It is also an object of the present invention to provide an arrangementfor determining the content of chemical elements in specimens thatrequire no special techniques for their preparation.

It is a still further object of the present invention to provide anarrangement that is reliable and convenient for use under fieldconditions.

SUMMARY OF THE INVENTION It is a specific object of the presentinvention to provide a method for determining the content of chemicalelements,

isotopes or compounds thereof in specimens, wherein use is made of theeffect of recoilless resonance absorption or scattering of gamma-rays.The procedure involves, according to the invention, measuring, in thecourse of irradiation, a quantity that is proportional to the content ofa chemical element, an isotope or compounds thereof in a test specimen,said quantity being represented by the following equation:

where N\ is the number of pulses recorded with the radiation source andtest specimen oscillating with in respect to each other, the amplitudeand frequency of oscillations being selected so as to disturb theresonance conditions for most of the oscillation period;

N,, is the number of pulses recorded with the gamma-ray source andspecimen it rest with respect to each other;

N,, is the number of pulses recorded with the gamma-ray source and testspecimen at rest with respect to each other, the resonance component ofradiation from the source being filtered off,

and thereafter determining the quantity of an element, an isotope orcompounds thereof in the test specimen by means of a'calibration curve.

It is sound practice to plot the calibration curve by the techniquesdescribed hereinabove so that said curve will express the dependence ofthequantities that are proportional to the content of a chemicalelement, an isotope or compounds thereof in reference specimenscontaining a specified amount of the element being'analyzed,'isotope orcompounds thereof, upon the specified amounts of the chemical element,isotope or compounds thereofin said specimens.

Reference specimens may be prepared by compressing a mixture of anorganic compound with the specified amount of the'chemically pureelement being analyzed, isotope or compounds thereof, said treatmentbeing carried out so as to cause no lattice disturbance.

In the arrangement for accomplishing the present method of determiningthe content of chemical elements, isotopes or compounds thereof in testspecimens which comprises a resonance gamma-ray source, a detector forrecording gamma-quanta passingv through or scattered by a test specimen,and a mechanism for setting the source and the specimen in relativemotion use is made, according to the present invention, of a resonanceradiation total absorption filter placed between said source and saiddetector, whilst the displacement mechanism is essentially a vibrator.

In the preferred embodiment, the total absorption filter may be made inthe form ofa plate manufactured by compressing a mixture of an organiccompound with a chemically pure isotope of the element being analyzed orcompounds thereof, said treatment being carried out so as to cause nolattice distortion.

The vibrator may be made in the form ofa piezocrystal rigidly linked tothe gamma-ray source.

DETAILED DESCRIPTION OF INVENTION Other objects and-advantages of thepresent invention will become apparent from the'examples embodying saidinvention and the appended drawings, wherein:

FIGJI shows a device for recording the gamma-ray radianuclei of theisotope being analyzed. The present invention relates specifically tothe method for determining SnO in rock specimens and also to thearrangement for accomplishing said method.

Presented in FIG. 1 is a schematic diagram of the arrangement forcarrying out the method of quantitative estimation of cassiterite (SnOin powder samples of rocks, The arrangement comprises a measuring headand a recording unit.

The measuring head incorporates source 1 (FIG. 1) of resonance gamma-rayradiation, manufactured of Sn'"0 powder on a Plexiglas disc, affixed tobimorphous piezoelectric element 2 made of polarized leadzirconate-titanate ceramics, one end of said piezoelectric element beingrigidly fixed. The radiation source is housed in leadcontainer-collimator 3, which affords shielding and also collimates thegamma-ray beam. To absorb the background characteristic radiation of thesource, use is made of palladium filter 4. Powder specimen 5 of thespecimen being examined is placed in special-type holder 6, which istransparent to gamma-rays. The radiation detector, which recordsgamma-quanta transmitted through test specimen 5, comprises thin NaI(Tl)crystal 7 and photoelectronic multiplier 8. From the detector, thesignal passes via stage 9 of an emitting repeater and connecting cable10 to recording unit 11. Disposed ahead of the detector, is resonanceradiation total absorption filter 12.

Recording unit 11 incorporates an amplifier, a differentialdiscriminator, a scaling circuit, and an electromechanical pulse counter(not shown). Starting, stopping, and resetting of the entire countingcircuit are synchronized with starting, stopping, and resetting of astop-watch also incorporated in the recording unit (not shown). Inaddition, the recording unit contains a battery power supply for theentire arrangement, a power pack, and a sine-wave generator for feedingthe piezoelectric element (all not shown With radiation source 1stationary, gamma-quanta on passing through test specimen 5 undergoresonance absorption by Sn nuclei contained in Sno so that the number ofpulses N recorded by the recording unit over a given period oftime willvary with the content of SnO in the test specimen. When sinusoidalvoltage is applied to piezoelectric element 2, said element togetherwith the radiation source starts oscillating with a resultant change inthe energy of gamma-quanta because of the Doppler effect. Resonanceabsorption on the Sn" nuclei will be practically nonexistent, providedthe amplitude and frequency of the radiation source oscillations areadequate for disturbing the resonance conditions for most of theoscillation period, and the recording unit will record N'\ pulses overthe same period of time. Both said measurements are preformed with nodetachable total absorption filter I2 ahead ofthe detector.

Then, ahead of the detector there is placed filter 12. which effectstotal absorption of the resonance radiation from Sn""0 The recordingunit will record, over the same period of time, N,, pulses correspondingto the magnitude of background radiation sensed by the detector, saidbackground radiation being associated with radiation due to otherspectral lines ofthe source and, with the characteristic radiationofelements in the mother rock, etc.

When N,,, N,,, and N have been measured, the quantity 6 proportional tothe content of SnO in test specimen 5, will be calculated by recordingunit I I from the following equation:

'identical to that disclosed hereinabove for measurements on testspecimens, except that reference specimens are substitutetl for restspecimen 5 in the present arrangement (FIG. I t.

To determine the content of SnO in the test specimen, the procedureinvolves calculating the value of e for the test specimen, said valuebeing proportional to the content of SnO in said test specimen, andmaking use of the calibration curve presented above to find the SnOcontent sought.

Reference specimens may be plates obtained by compressing a mixture ofan organic compound with a specified, highly accurate amount ofchemically pure SnO provided the compression involves no latticedisturbance.

The total absorption filter comprises a plate made by compressing amixture of an organic compound with SN' O in an amount adequate for thetotal absorption of resonance gamma-ray radiation.

An analogous procedure could be followed for the determination of thecontent of SnO directly in the surface layers of test specimens 13 (FIG.3). Here gamma-ray radiation from source 1, which is applied tobimorphous piezoelectric element 2 and placed in container-collimatorl3, falls onto the surface of test specimen l3, and the gamma-quantascattered by the surface of test specimen 13 are recorded by a detectorcomprised of thin NaI(Tl) crystal 7 and photoelectric multiplier 8'.Disposed ahead of said detector is detachable, resonance radiation totalabsorption filter 12', and from said detector the signal is fed viastage 9 of an emitting repeater and connecting cable 10' to recordingunit 11.

In the embodiment of the present arrangement described hereinabove, thevalue of e, which is proportional to the content of SnO in the testspecimen, is derived from the following equation:

When use is made ofa Sn" 'O source having an activity on the order ofamillicurie, the present arrangements (FIG. land 2) make it possible todetermine the content of tin in cassiterite within l0 minutes to 0.055percent, an accuracy which compares favorably with that obtainable bychemical methods of analysis.

Although the present invention has been described with reference to apreferred embodiment thereof, it is apparent that various alternationsand modifications may be made therein without deviating from the spiritand scope of the invention, as those skilled in the art will readilyunderstand.

Such alterations and modifications shall be considered as falling withinthe spirit and scope of the invention as set forth in the appendedclaims.

We claim:

I. A method of determining the content in specimens of a member selectedfrom the group consisting of chemical elements, isotopes and compoundsthereof, consisting essentially in that the specimen is irradiated withgamma-quanta capable of being resonantly absorbed and dispersed by anisotope of the element being determined, determining the ratio of thedifference of the number of gamma-quanta registered when the source andthe specimen oscillate with respect to each other with an amplitude andfrequency of oscillations sufficient for violating the conditions ofresonance for the greatest part of the period of oscillations, and thenumber registered when the source and the specimen are at rest withrespect to each other, to the said nun oer of gamma-quanta registeredwhen the source and the specimen oscillate with respect to each other,or due to the background induced by the nonresonant component of theradiation of the source, and employing said ratio to compute thequantitative content of the said element in the said specimen by meansof a graduating relationship.

2. A method according to claim 1 wherein said member is s tmo 3. Amethod of determining the content in specimens of a member selected fromthe group consisting of chemical elements, isotopes and compoundsthereof, consisting essentially in that the specimen is irradiated withgamma-quanta capable of being resonantly absorbed and dispersed by anisotope of the element being determined, determining the ratio of thedifference of the number of gamma-quanta registered when the source andthe specimen oscillate with respect to each other with an amplitude andfrequency of oscillations sufficient for violating the conditions ofresonance for the greatest part of the period of oscillations, and thenumber registered when the source and the specimen are at rest withrespect to each other, to the said number of gamma-quanta registeredwhen the source and the specimen oscillate with respect to each'other,due to the background induced by the nonresonant component of theradiation of the source, applying a graduating relationship as therelationship of the said ratios of standard specimens with a givenquantity of the said member to the said quantities of the said member inthe standard specimens, and utilizing the said ratio to compute thequantitative content of the said element in the specimen beinginvestigated with the aid of the said graduating relationship.

4. A method of determining the content in specimens of a member selectedfrom the group consisting of chemical elements, isotopes and compoundsthereof, consisting essentially in that the specimen is irradiated withgamma-quanta capable of being resonantly absorbed and dispersed by anisotope of the element being determined, determining the ratio of thedifference of the number of gamma-quanta registered when the source andthe specimen oscillate with respect to each other with in amplitude andfrequency of oscillations sufficient for violating the conditions ofresonance for the greatest part of the period of oscillations, and thenumber registered when the source and the specimen are at rest withrespect to each other, to the said number of gamma-quanta registeredwhen the source and the specimen oscillate with respect to each other,due to the background induced by the nonresonant component of theradiation of the source, pressing standard specimens from a mixture ofan organic substance with a given quantity of the chemically pure saidmember without violation of its crystalline lattice, applying agraduating relationship as the relationship of the said ratios of saidstandard specimens to the said given quantities of the said member inthe said standard-specimens, and utilizing the said ratio to compute thequantitative content of the said element in the specimen beinginvestigated with the aid of the said graduating relationship.

5. An arrangement for determining the content in specimens of a memberselected from the group consisting of chemical elements, isotopes, orcompounds thereof, comprising a source of resonance radiation; adetector for registering gamma-quanta from said source that have passedthrough the specimen being investigated, or have been dispersed by it; afilter for total absorption of the resonance radiation in the form ofaplate made by pressing a mixture of an organic substance with achemically'pure isotope of the said member being investigated withoutviolation of their crystalline lattice, arranged between said source ofresonance radiation and the specimen being investigated.

6. An arrangement for determining the content ofa member selected fromthe group consisting of elements, isotopes, and compounds thereof, inspecimens which comprises a resonance radiation source; a detector forrecording gammaquanta from said source that have passed through or havebeen scattered by a said specimen; a resonance radiation totalabsorption filter disposed between said resonance radiation source andsaid detector; and a vibrator means comprising a piezoelectric elementwhich is rigidly coupled to said resonance radiation source and servesto set said source in motion relative to the test specimen.

2. A method according to claim 1 wherein said member is Sn11902.
 3. Amethod of determining the content in specimens of a member selected fromthe group consisting of chemical elements, isotopes and compoundsthereof, consisting essentially in that the specimen is irradiated withgamma-quanta capable of being resonantly absorbed and dispersed by anisotope of the element being determined, determining the ratio of thedifference of the number of gamma-quanta registered when the source andthe specimen oscillate with respect to each other with an amplitude andfrequency of oscillations sufficient for violating the conditions ofresonance for the greatest part of the period of oscillations, and thenumber registered when the source and the specimen are at rest withrespect to each other, to the said number of gamma-quanta registeredwhen the source and the specimen oscillate with respect to each other,due to the background induced by the nonresonant component of theradiation of the source, applying a graduating relationship as therelationship of the said ratios of standard specimens with a givenquantity of the said member to the said quantities of the said member inthe standard specimens, and utilizing the said ratio to compute thequantitative content of the said element in the specimen beinginvestigated with the aid of the said graduating relationship.
 4. Amethod of determining the content in specimens of a member selected fromthe group consisting of chemical elements, isotopes and compoundsthereof, consisting essentially in that the specimen is irradiated withgamma-quanta capable of being resonantly absorbed and dispersed by anisotope of the element being determined, determining the ratio of thedifference of the number of gamma-quanta registered when the source andthe specimen oscillate with respect to each other with in amplitude andfrequency of oscillations sufficient for violating the conditions ofresonance for the greatest part of the period of oscillations, and thenumber registered when the source and the specimen are at rest withrespect to each other, to the said number of gamma-quanta registeredwhen the source and the specimen oscillate with respect to each other,due to the background induced by the nonresonant component of theradiation of the source, pressing standard specimens from a mixture ofan organic substance with a given quantity of the chemically pure saidmember without violation of its crystalline lattice, applying agraduating relationship as the relationship of the said ratios of saidstandard specimens to the said given quantities of the said member inthe said standard specimens, and utilizing the said ratio to compute thequantitative content of the said element in the specimen beinginvestigated with the aid of the said graduating relationship.
 5. Anarrangement for determining the content in specimens of a memberselected from the group consisting of chemical elements, isotopes, orcompounds thereof, comprising a source of resonance radiation; adetector for registering gamma-quanta from said source that have passedthrough the specimen being investigated, or have been dispersed by it; afilter for total absorption of the resonance radiation in the form of aplate made by pressing a mixture of an organic substance with achemically pure isotope of the said member being investigated withoutviolation of their crystalline lattice, arranged between said source ofresonance radiation and the specimen being investigated.
 6. Anarrangement for determining the content of a member selected from thegroup consisting of elements, isotopes, and compounds thereof, inspecimens which comprises a resonance radiation source; a detector forrecording gamma-quanta from said source that have passed through or havebeen scattered by a said specimen; a resonance radiation totalabsorption filter disposed between said resonance radiation source andsaid detector; and a vibrator means comprising a piezoelectric elementwhich is rigidly coupled to said resonance radiation source and servesto set said source in motion relative to the test specimen.